Patent application FR 2 881 366 in the name of SETI TEC describes a drilling device including a drive gearwheel for driving a bit-carrier spindle in rotation and an advance gearwheel connected to the bit-carrier spindle via a threaded connection.
A similar device is shown in FIG. 1. In this figure the numerical references are the same as those used below for referring to component parts that are identical or similar.
Vibratory drilling devices are also known from the following publications: WO 2008/000935 A1, DE 10 2005 002 462 B4, U.S. Pat. No. 7,510,024 B2, FR 2 907 695, and US 2007/209813.
Vibratory assistance serves to break up swarf and to increase the quality of drilled holes by eliminating the risk of clogging, to increase the lifetime of tools, and to make the method more reliable.
In publications FR 2 907 695, U.S. Pat. No. 7,510,024, and US 2007/209813, the oscillations are generated by cams without rolling members. That gives rise to friction on the cams, thereby generating heat and noise. In addition, the optimum vibratory frequency for good fragmentation of swarf is not always obtained because the frequency is an integer multiple of the speed of rotation differential between the advance gearwheel and either the spindle or the housing, which differential is directly related to the number of oscillations of the cam.
In patent DE 10 2005/002462, a spring exerts a return force on a rolling bearing that includes a raceway that is undulating in the advance direction of the drill bit for the purpose of producing axial vibration. In the event of high axial pressure on the drill bit, the rolling members can cease to roll on the undulating raceway and the bit can cease to oscillate. In order to avoid that drawback, the spring must be very stiff, which can lead to the bearing being overdimensioned. That gives rise to increased costs and size.
Furthermore, the device is fitted to the end of the spindle, under the advance system, thereby adding to overall size and leading to greater complexity.
There exists a need to further improve drilling devices, in particular those for machining aviation workpieces of large dimensions, such as for example fuselage or wing parts.